Urinary system Flashcards
Urinary system consists of
Includes kidneys, ureters, urinary bladder, and urethra
Functions of kidneys
Blood filtration, reabsorption and secretion
Acid-base balance
Fluid-electrolyte balance
Hormone production
Blood pressure regulation
Blood filtration, reabsorption and secretion in the kidneys
Through altering plasma composition by
Filtering plasma constituents from the blood
Selectively reabsorbing water and useful components
Secreting waste products as urine
Acid base balance is done by the kidneys by
Eliminates hydrogen and bicarbonate ions in urine
How do kidneys regulate acid-base balance
Controls water and electrolytes, removing them from blood to equal amount being put in
Correct water to maintain healthy internal environment, through
Diuresis (excess water so more urine formed)
Oliguria (insufficiency of water so less urine formed)
Anuria (deficiency in water so no urine formed)
Under hormonal control (function of the endocrine system) – ADH and aldosterone
What hormones are produced in kidneys
Renin: to help increase blood pressure if drops through the renin-angiotensin system
Erythropoietin: to increase RBC production if hypoxic
Prostaglandins: to help maintain renal perfusion
How does Kidney help with blood pressure regulation
Receptor monitor blood pressure
Renin
To help increase blood pressure when BP is low, through the renin-angiotensin system
the nephron of the kidney is and does what
The nephron is the functional unit
It is a microscopic, epithelial structure
Consists of a blood filtration unit attached to a long tube that absorbs and secretes to deliver urine as its end product
In order, the parts of the nephron are:
Bowman’s capsule (filtration)
Proximal Convoluted Tubule
Loop of Henle
Distal convoluted tubule
Collecting Duct
Where are the kidneys located
The kidneys are located in the abdominal cavity just to each side of the midline and are retroperitoneal (behind/outside of peritoneal cavity)
Generally, the right kidney is more cranially and dorsally than the left kidney
What does the kidney look like
A thick layer of fat surrounds and protects the kidneys
Called peritoneal fat
This allows us to visualize the kidneys on abdominal x-rays
Generally, the shape and color of kidney beans and smooth-surfaced
Capsule of the kidney is
a thin, but tough, connective tissue layer which surrounds the kidney
Hilus is what of the kidney
Located in the depression on the medial side of the kidney
The renal artery and nerves enter, and the ureter, renal vein and lymphatic vessels leave at the hilus
Renal pelvis is the
the expanded part of the ureter just inside the hilus
Receives urine from the collecting tubules of the kidney
Not found in cattle
Renal cortex is located
immediately beneath the capsule
Renal medulla is located and contains
Inner layer of kidney
Appears striated due to the arrangement of the collecting tubules
Also contains some loops of Henle (which contain the most concentrated fluid)
Renal cortex is
(aka papilla):
Ridge that projects into the renal pelvis .
The collecting tubules of medulla empty here.
Calyces are and do what
Funnels that medulla projects into
Direct fluid straight into the ureter
What does the bovine kidney look like
Kidneys are lobulated and do not have a renal pelvis or crest
Instead the ureter branches into each lobe and forms calyces, (calyx singular)
Porcine kidney shape
Also has calyces. Funnels fluid into the renal pelvis.
Nerve supply to the kidney
Supplied mainly by sympathetic nerves from the autonomic nervous system.
Sympathetic stimulation reduces renal blood flow
Not necessary for function: can rely on other controls (for example, if transplanted)
How much blood does the kidney get
The kidneys receive approximately ¼ of the cardiac output and convert about one thousandth of this into urine.
Renal artery is and goes where
enters the hilus
divide into smaller and smaller branches
become the afferent glomerular arterioles
What goes the afferent glomerular arterioles branch into
The afferent glomerular arterioles branch to form the glomerular capillary network of the renal glomerulus
Glomerular capillaries does what
Filter out some of the water and small molecules from the blood
The only capillary network in the body where blood is oxygenated going into and coming out
The efferent arteriole: leaves what
leaves each glomerulus
Surrounds the rest of the nephron
From capillary networks around the tubules and lupus of Henle
Where does the blood go from the kidney
These capillary networks then reform as veins
Getting larger and larger
Become the renal vein passing out of the kidney at the hilus
Drain into the cranial vena cava
When blood is within the capillary networks of the nephron it does what
Waste and excesses are removed from the blood into the nephron
Water and useful constituents can be reabsorbed from the filtrate into the blood.
Ureters are
Muscular tubes
Carry urine from the kidneys to the bladder
They exit the kidney at the hilus
Enter the urinary bladder near the neck
Enter bladder at an oblique angle
When it is full, the ureter collapses to prevent backflow of urine
Ureter wall 3 layers
Outer fibrous
Middle smooth muscle
Inner transitional epithelium (allows stretching as urine passes through)
What is the function of the ureters
Functions to move urine from kidneys to bladder through peristalsis
Can continue to move urine into a full bladder with a collapsed ureter because of the peristaltic movements
Anatomy of urinary bladder
Hollow muscular organ capable of stretching
Size and position vary, depending on fullness
Empty – will be almost inside the pelvis, thick walls
Filling – pear-shaped, extends cranially, thin walls
Lined with transitional epithelium
Has layers of smooth muscle
At the neck, a sphincter of skeletal muscles allows voluntary control of urination
Trigone: the area between urethra and ureteral opening. Landmark for ultrasound
Bladder function
Collect, store, release urine
Urine is formed continuously, released intermittently
Three steps to urination
Urine accumulation
Muscle contraction
Sphincter muscle control: voluntary release of skeletal muscles at sphincter.
Urine accumulation in the bladder
Bladder fills until critical point
Activates stretch receptors
Muscle contraction for urination
Spinal reflex activated
Causes contraction of smooth muscles
Results in sensation of needing to urinate
Sphincter muscle control: voluntary release of skeletal muscles at sphincter for urination
If wait too long, continuing filling of bladder may result in ‘leakage’
Loss of voluntary control of the bladder is known as urinary incontinence (inability to urinate when and/or where desired)
***a full bladder is very prone to rupture!!! Use care if palpating!
Anatomy of the urethra
Continues from neck of the bladder
Has transitional epithelium
Short & straight in females
Opens onto the floor of the vestibule
Longer and curved in males
Runs down center of penis
Carries urine out of the body from the bladder
In males, also carries semen during ejaculation and is surrounded by a urethral muscle.
Kidneys are composed of what and what do they do
Kidneys are composed of hundreds of thousands of microscopic structures called nephrons
Basic functional unit of kidney
Have different parts that specialize in filtration, reabsorption, and secretion.
Parts of a nephron
Renal corpuscle
Proximal Convoluted Tubule
Loop of henle
Distal Convoluted Tubule
Renal corpuscle is composed of
In the kidney cortex
Composed of:
Glomerulus: tiny capillary network
Bowman’s capsule: double walled capsule surrounding the glomerulus
Inner layer lines the capillaries
The visceral layer
Outer layer surrounds it
The parietal layer
Space between the 2 layers an extension of the proximal tubule
Capsular space - continues with the proximal convoluted tubule
Function of the renal corpuscle
Glomerulus filters blood through the capillaries
Creates glomerular filtrate
Collects filtrate in Bowman’s capsule
Proximal convoluted tubule is
Highly coiled (hence the name)
In the renal cortex
Continuous with Bowman’s capsule
Lined with cuboidal epithelial cells with microvilli
Increases surface area x20 to have the microvilli
Lined with simple, cuboidal epithelial cells with microvilli- to increase the surface area
Function of the proximal convoluted tubule
Reabsorption and secretion
Responsible for about 65% of the total reabsorption
80% of all water, sodium, chloride, and bicarbonate absorption
100% of the glucose and amino acid absorption
Loop of henle is and where it is
U-shaped
Extends from within the cortex into the medulla and returns to the cortex
Divided into the descending and ascending limbs
Smaller diameter than rest of renal tubule
Function of the loop of henle
Reabsorption
Sodium exchanged for other ions
Water is reabsorbed
Creates a concentration gradient that favors reabsorption of water
Distal convoluted tubule is
In the cortex
Coiled
Joins a collecting duct, along with other nephrons
Distal convoluted tubule function
Reabsorption and secretion
Sodium exchange for other ions
Nephrons join and continue
Nephrons join to common collecting ducts, which extend into the renal papilla
Collecting ducts are important for potassium levels, secretion of hydrogen and ammonia and acid base balance
Antidiuretic hormone (ADH) has its greatest effect here
Filtration of blood occurs in
Renal corpuscle
Renal capillaries differ from normal capillaries because they:
Connect 2 small arterioles
Have small pores to increase fluid leakage
Not big enough to allow proteins or cells to leak out.
So, protein in the urine on urinalysis is a sign of glomerular disease
Renal capillaries differ from normal capillaries because
Are under high pressure
Especially since the afferent arteriole is larger than the efferent arteriole
Causes pressure build-up in glomerulus
Forces fluid out – called filtration
Collects in Bowman’s capsule
GFR is
glomerular filtration rate (ml per minute)
How fast plasma is filtered
Depends on the rate of flow through the kidney
Blood pressure is critical for maintaining GFR
Needs to keep mean arterial pressure about 60 mm Hg
Glomerular filtrate contains what and for what reasons
Glomerular filtrate contains many substances the body needs to maintain balance of nutrients, minerals, electrolytes and acid base
i.e. sodium, potassium, calcium, magnesium, glucose, amino acids, chloride, bicarbonate, and water
Normally ABOUT 99% of water is reabsorbed.
Reabsorption occurs in
Occurs in Proximal Convoluted Tubule (PCT)
Proximal Convoluted Tubule (PCT) does what for reabsorption
Passive diffusion or active transport: substances move through the tubular epithelium, interstitial space, and into the peritubular capillaries
Sodium co-transport occurs:
Active transport of sodium out of tubular epithelium cell by a carrier protein on the basement cell membrane – uses energy
Co-transport of sodium into cells with glucose and amino acids
Conserves glucose and amino acids
What is the limit on the amount of glucose in the body called
there is a limit on the amount of glucose the body can reabsorb
Called the renal threshold
If blood glucose levels exceed the threshold, some glucose will remain in the urine
Occurs with diabetes mellitus and other conditions causing high blood glucose
Can cause an osmotic diuresis
Leading to clinical symptoms of PU/PD
Reabsorption in the loop of Henle and DCT
Sodium is reabsorbed in exchange for hydrogen, ammonium, or potassium ion
Chloride follows sodium due to electrical gradient
Controlled by aldosterone (mineralocorticoid from the adrenal cortex)
What happens after ions move out of the lumen
Potassium, calcium and magnesium are also reabsorbed
Once ions have moved out of the lumen, water follows by osmosis
Much of this occurs in the DCT and collecting ducts
This increases the concentration of the remaining molecules in the filtrate within the lumen
Some substances, like urea, will increase concentration to the point of being more concentrated than the blood
Some reabsorption of urea will take place here
This is minor and keeps urea levels in body at normal levels
Secretion is primarily occurred in
PCT for substances like histamine, uric acid, creatine and hydrogen
DCT for substances like hydrogen (more), potassium, and ammonia
Aldosterone helps promote secretion of potassium and reabsorption of sodium in DCT
Secretions of the kidneys steps
Also secretes drugs like penicillin and some sulfonamides
Substances are moved from peritubular capillaries, through the interstitial fluid and tubular epithelial cells to the lumen
Secretion is particular important for molecules that are not filtered in the glomerulus
Urine volume regulation is controlled by
Primarily controlled by antidiuretic hormone (ADH) from posterior pituitary and aldosterone from adrenal cortex
ADH does what for urine regulation
Increases water reabsorption from DCT and collecting ducts
Increased number of water pores in cells
If levels of ADH are too low, can result in inadequate reabsorption of water
This causes high volume of urine (poor concentration, low SG) and increased drinking to compensate for water loss (PU/PD)
Called diabetes insipidus (differentiate from DM by glucose in urine)
Aldosterone does what for urine reagulation
Increases sodium reabsorption from DCT and collecting ducts
Creates osmotic imbalance
Draws water back into the blood (BUT, requires presence of ADH to occur!!)
Water intake is regulated by
Water intake is regulated by a thirst center in the hypothalamus
Responds to blood pressure and water concentration in the blood
